Firefox 3.0 and self-signed certificates

Hello, Michael Barrett here.

I read a rather worrying criticism of Firefox 3.0 on “Risks” the other day, which made me realize that perhaps there isn’t a common agreement amongst the infosec industry about the threatscape and how we should prioritize our response to them. Specifically, the complaint against Firefox 3.0 is that the user experience has been deliberately crafted to make it hard to accept self-signed certificates. The argument is that there are times when simply establishing an encrypted tunnel (i.e. an SSL session) is all that’s needed.

 

I certainly wouldn’t argue that encryption is unnecessary, just that the threat has changed.  While our old “friend” Mallory isn’t particularly busy these days, it’s pretty clear that he’d be having a field day if he could easily penetrate communications across the Internet. The attacker however is no longer limited to passive eavesdropping. Modern attacks use active DNS spoofing, active MITM attacks and the like, on public networks.  The main threats these days are against the weakest link in the chain – the end user. That’s why phishing is such a popular method of e-crime – it’s simple and it works. It relies completely on the gullibility of users in clicking on links in e-mails apparently from organizations with whom they have a relationship.

 

However, it’s equally clear that almost everyone who wants to communicate securely using a browser can afford an SSL certificate from CAs such as GoDaddy, Thawte, etc. The cost of single certificates from these sources can only be described as nominal.

 

My company is a major target of phishing, and as such we’ve spent quite a bit of time researching what anti-phishing approaches work We published a whitepaper on this topic (which can be found on the company blog at www.thepaypalblog.com), which explains this in detail. However, a couple of relevant conclusions are that: 1) the vast majority of users simply want to be protected, 2) there’s no single “silver bullet”, and 3) that what we describe as “safer browsers” such as IE 7, and Firefox 3.0 are a significant part of the solution based on their improvements in user visible security indicators and secure-by-default behaviors.

 

I conflated two or three separate ideas in that last sentence, and I should explain them. The general logic is that most users should never be presented with a security dialog that gives them a choice – if they are, there’s typically at least a 50:50 chance that the wrong decision will be made. Instead, the browser should make the decision for them. However, in the case of self-signed certificates it’s almost impossible to see how any technology can disambiguate between legitimate uses and criminal ones.

 

When viewed through this lens, the changes to the Firefox user experience for self-signed certificates makes perfect sense. It’s not that self-signed certificates are impossible to use – but for most users, the experience will be such that they won’t accept them. In the unsafe world in which we live, that will be the right choice. For organizations which wish to use self-signed certs internally, it is still technically possible – but it will require either explicit user training, or deployment of pre-installed certificates on PCs.

 

I should also add that the major security features which have been added into the most recent browser versions (and which we believe are necessary in order to be considered ‘safer’) are exactly those which impact this area. That is: support for Extended Validation certificates, which make it clear to end users whose web site they’re on; and support for spoof-site black lists, so that users can’t easily reach spoof-sites.

 

While I’m personally a great supporter of the “Risks” list, I think it’s important that the infosec industry speaks with good consensus about risks. In this case, I believe that the criticism of Firefox 3.0 was simply misguided and ill-informed. This is not helpful.

 

Comments

[Mike Beltzner]

Hi Michael,

You might be interested to read Johnathan Nightingale's response to the "Risks" piece here: at http://blog.johnath.com/2008/08/05/ssl-question-corner/

I worked with Johnathan, Nelson Boylard, Kai Engert, Bob Lord and others on the new SSL behaviours in Firefox 3, and while (as Johnathan admits) they're not perfect, we share your belief that they are better than they were before.